A four-wheel-drive vehicle is known that has a pair of left and right main drive wheels to which power of a drive power source is transmitted and a pair of left and right auxiliary drive wheels to which a portion of the power of the drive power source is transmitted via a transmission member during four-wheel-drive running mode. Regarding such a four-wheel-drive vehicle, a drive mode switching device is proposed and (a) the drive mode switching device has a first connecting/disconnecting device connecting and disconnecting power transmission between the drive power source and the transmission member and a second connecting/disconnecting device connecting and disconnecting power transmission between the transmission member and the auxiliary drive wheels such that one of the first and second connecting/disconnecting devices is a friction engagement clutch capable of adjusting an engagement torque while the other is a dog clutch, and (b) the drive mode switching device comprises a four-wheel switching control portion that controls the engagement torque of the friction engagement clutch when switching to four-wheel-drive running mode in which four wheels including the auxiliary drive wheels are driven during two-wheel-drive running mode in which only the main drive wheels are rotationally driven with both the friction engagement clutch and the dog clutch disconnected and thereby increases the rotation speed of the transmission member to connect the dog clutch after synchronization in which a differential rotation speed of the dog clutch becomes equal to or less than a predetermined value. A four-wheel-drive vehicle described in Patent Document 1 is an example thereof, and since the rotation of the transmission member (a front propeller shaft 13) is stopped during the two-wheel-drive running mode, excellent fuel consumption performance can be obtained. Additionally, in Patent Document 1, to suppress a deceleration shock (change in vehicle acceleration/deceleration) due to a rotational load of the transmission member at the time of synchronous control of increasing the rotation speed of the transmission member (the front propeller shaft 13) by controlling the engagement torque of the friction engagement clutch (an electric control coupling 12), a target synchronization time is set based on an accelerator operation amount, a vehicle speed, or a steering angle, and the engagement torque of the friction engagement clutch is controlled such that the synchronization is achieved in the target synchronization time.